The present invention relates to an hydraulic device for passing waste water from a draining unit, such as a sink into a sewer. Such devices are known which comprise a cylindrical body for receiving a water seal therein, an inlet pipe extending from the draining unit into the cylindrical body, an outlet pipe extending from the cylindrical body and adapted to be connected to a sewer, a cover extending over the cylindrical body and defining with the cylindrical body a peripheral air inlet, and an annular valve resting over the peripheral air inlet. The valve blocks the passage of air out of the cylindrical body when air pressure in the outlet pipe is balanced with respect to the pressure exterior of the cylindrical body and when there is an overpressure in the outlet pipe.
Such a device in which an automatic air valve device and a siphon are combined so that their functions are complementary, is described in U.S. Pat. No. 4,212,314 granted to K. S. B. Ericson, one of the present inventors.